The necessity for providing sewage treatment plants to clean and purify water discharged from homes and factories is well known. The function of a sewage treatment facility is to receive raw sewage (water containing waste material) as discharged from a city sewerage system and clean it to ultimately produce purified water. This is accomplished through a series of biological and mechanical processes.
In a typical water treatment facility, the raw sewage is received from the sewerage system and passed through a coarse screen to remove large pieces of matter. The sewage is next directed to one or more primary sedimentation tanks or clarifiers. The sewage remains in primary sedimentation for a period of time sufficient to allow the majority of the heavy matter to settle to the bottom of the tank forming sludge. The sludge is removed for "digestion" by micro-organisms. The digested sludge is dried and can be used as compost or fertilizer. The remaining liquid is treated in a second biological system to remove ammonia. The liquid from this treatment is then aerated and passed into final sedimentation water treatment tanks to remove any remaining solid material.
Water treatment tank configurations vary with each treatment facility application. This notwithstanding, most final sedimentation water treatment tanks are round. This simplifies automatic skimming, churning and/or bottom scraping operations. More specifically, by eliminating inaccessible corners and providing uniform surfaces a revolving arm or skimmer blade can provide complete and efficient churning and prevent sludge buildup.
During operation of one type of water treatment tank sediment containing water enters the center of the tank. In a continuous process, the lighter clean water is effectively decanted from the heavier sediment containing water. More particularly, the clean water is displaced from the tank by the constant flow of sediment containing water into the tank. The displaced clean water is forced to flow under a baffle plate for collecting floating scum and then over a weir, ultimately entering a clean water flow channel. The clean water flow channel directs the water to the next treatment stage where it is chlorinated and further made safe to be discharged into a river or stream.
As is known in the art, the outdoor exposure of the water treatment tanks in direct sunlight encourages the growth of algae. This growth is most prevalent on the baffle, weir, spillway and clean water flow channel. Disadvantageously, algae growth on these members inhibits the flow of clean water from the tank. Further, the algae can be carried in thick masses and high concentrations in the clean water being discharged from the final treatment tank. When this occurs, large concentrations of chlorine are required to kill the algae. Because chlorine is relatively expensive, it is desirable to avoid this problem.
To date, removing the algae from the baffle, weir, spillway and clean water flow channel has been done primarily by scrubbing the tank structure with brushes manipulated by hand. Because the final treatment tanks are quite large, this naturally, is a labor intensive and tedious process, involving a large expenditure of man-hours and cost outlay. Additionally, the algae removing process must be done frequently, further adding to the cost.
This can be dramatically demonstrated by considering the following example. It takes approximately eight man hours to manually clean the algae from the baffle, weir, spillway and clean water flow channel of a water treatment tank having a diameter of approximately 60 feet. At a labor wage rate of eight dollars per hour, it costs approximately sixty four dollars to clean one tank. Preferably, such a cleaning is performed once a week on average (perhaps more often in summer and less often in winter, depending on weather conditions). This represents a cost of $3,328 per year to clean just one treatment tank. Of course, most facilities include more than one tank. For example, a four tank facility may spend as much as $13,312 in labor alone to clean the algae from its tanks each year. Any substantial reduction in this expense is desirable.
A need therefore exists for an algae removal or cleaning apparatus for use in sewage treatment facilities. Such an apparatus should be reliable and effective in eliminating the buildup of algae while substantially reducing clean up costs.